The Revelator woofers and subwoofers features very rigid cones in paper or aluminium that operates as a piston over a wide frequency range, in combination with Scan-Speaks low-loss linear suspension and the patented Symmetrical Drive (SD-1) it results in very low distortion and a smooth and well behaved frequency response as well as perfect transient reproduction.
Datasheet: Datasheet 22W/8857T00

Size (inches): 8
Fs (Hz): 23
Re (ohms): 6.2
Sensitivity (dB): 86
Qt: 0.30
VAS (ltr.): 87.7
Xmax ± (mm): 9

Here you can soon find DIY kits for this driver.